Damage-Plastic Constitutive Model of Thin-Walled Circular Steel Tubes for Space Structures

Abstract

In this paper, we establish a coupled damage-plastic constitutive model in the scheme of small deformation assumption, based on a continuum damage mechanics model proposed by Lemaitre, for the thin-walled circular steel tubes widely used in space structures. First, a new damage evolution law is developed for steel tubes. Then the isotropic damage-plastic constitutive model is created within the thermodynamics framework. In addition, the numerical integration algorithm for the proposed model is formulated based on the well-established operator split methodology and is implemented into ANSYS through the user-defined material subroutines. The uniaxial tension test and the spatial hysteresis experiment for thin-walled circular steel tubes are performed, which serves as calibration conditions for the new proposition. The model parameters are determined by the inverse optimization method and the least squares fitting method. Numerical results obtained from the proposed and Lemaitre model are compared with experimental data obtained by spatial hysteresis, and the predictive ability of both models is discussed in terms of the force-displacement hysteretic curves, the initiation and propagation of fracture, and the evolution of the damage variable. It is illustrated that the established model presents a good agreement with experimental observation. Furthermore, it performs a better prediction compared to Lemaitre’s model. Lemaitre’s model is able to predict the correct location for fracture onset but fails to capture the potential path of fracture propagation and the displacement at the fracture.